1. Technical Field
The invention relates to suspension systems, and in particular, to an air suspension system used for vehicles. More particularly, the invention relates to an air spring having an auxiliary reservoir formed integrally in one of the end members of the air spring, which communicates with the main air chamber of the air spring to enable the spring rate of the air spring to be varied by adjusting the volume of fluid in the auxiliary reservoir.
2. Background Information
Air springs have been used for a considerable number of years for various applications, including use in vehicles for absorbing road shock imparted onto the wheels of a vehicle upon the wheel encountering a projection or depression in the roadway. Some examples of such air springs are shown in U.S. Pat. Nos. 4,564,177, 4,718,650, 4,787,606 and 4,787,608.
Each air spring will have a specific spring rate depending upon the design of the air spring components and its size, which will provide various ride characteristics for the vehicle on which the particular air spring is mounted. One of the factors which determines the spring rate is the volume of air contained within the flexible sleeve or bellows of the air spring. Varying the volume of air in the flexible sleeve of the air spring enables various spring rates to be achieved. This is presently being accomplished by various means, such as by supplying or removing air into or from the air spring through various control valves, and by the use of auxiliary air reservoirs which are fluidly connected to the vehicle air spring, which is mounted on and extends between spaced structural members of the vehicle. When a vehicle wheel encounters a depression or projection in the roadway, air will be introduced into or removed from the vehicle air spring by means of an auxiliary reservoir to change the volume of air within the air spring, thereby changing the spring rate in order to provide the desired ride characteristics for the vehicle. The smaller the volume of the air chamber, firmer will be the ride provided thereby.
Heretofore, auxiliary reservoirs for air springs usually consisted of a remotely mounted reservoir which was connected by a hose or other fluid communication lines to the air chamber of the air spring. These remotely located reservoirs generally contained various means for adjusting the volume of the air chamber within the reservoir. Some examples of prior art air springs containing auxiliary reservoirs are shown in U.S. Pat. Nos. 2,115,072, 3,039,761, 4,159,105, 4,592,540, 4,743,000 and 5,169,129.
Although these remotely located reservoirs do provide for a variable spring rate air spring, it increases considerably the space required for mounting of the air suspension system, which in many vehicles is extremely limited. In all of these known prior art air spring suspension systems which use an auxiliary reservoir, the reservoir is located remote from the air spring and is not formed as an integral part thereof, as is the air spring of the present invention.
Examples of other prior art suspension systems and components therefor which are of interest to the present invention are shown in the following U.S. Patents.
U.S. Pat. No. 3,722,875 discloses a suspension unit that is adjustable through the use of counteracting air and liquid-filled bellows. Counteracting air bellows are separated from each other by a metal plate having an adjustable orifice positioned therein. The air-filled bellows are surrounded by liquid-filled bellows which are used for damping. Liquid bladders are positioned within the air bellows, so that they may be filled or evacuated with liquid, which will adjust the spring stiffness of the suspension device.
U.S. Pat. No. 4,325,541 discloses a telescopic shock absorber having load proportional limited damping. The telescopic shock absorber has a rolling diaphragm and an auxiliary diaphragm. The auxiliary diaphragm provides a variable damping force for the shock absorber.
U.S. Pat. No. 4,509,730 discloses a flexible wall spring damper which is formed from a side wall and a diaphragm which may be integrally formed with the side wall. A gas chamber is formed between the mounting member and the flexible diaphragm, and a valve allows the gas chamber to expand, thus affecting the spring rate of the spring damper.
U.S. Pat. No. 4,629,170 discloses an air spring having both inner and outer chambers. An inner membrane forms the inner chamber, and an outer membrane forms the outer chamber. Each of the chambers has continuously variable independent pressurization means which provide variable spring rate for the air spring.
U.S. Pat. No. 4,901,986 discloses a hydraulic engine mount that has various damping characteristics. An air transfer tube allows air to enter or leave a pneumatic bladder, and an inflation line delivers air from a variable pressure source to the bladder. The bladder moves towards and away from a piston surface upon deflation and inflation, thus varying the damping characteristics of the engine mount.
U.S. Pat. No. 4,974,820 shows a shock absorber which utilizes a main bellows and a sub-bellows. The sub-bellows provides varying natural resonance frequency for the main bellows as a result of the repercussion of the sub-bellows.
However, none of the prior art suspension systems, and in particular those which utilize an auxiliary reservoir, of which I am aware, forms the auxiliary reservoir as an integral part of the air spring.